Submersible pumps are widely used for pumping water, brine, and the like from deep wells. Generally, these pumps include motor and seal section units filled with a fluid which serves as a coolant and a lubricant for the moving parts of the motor. The seal section is usually disposed between the pump and the motor along the operating shaft and includes at least one rotary seal which prevents ingress of well fluid, i.e., water, brine, and the like and foreign matter therein, along the shaft. In addition, the seal section serves as a reservoir for the lubricating and cooling fluid and accommodates expansion and contraction of the fluid during on-and-off cycling of the motor. Necessarily, the fluid in the seal section is in communication with the well environment to accommodate fluid expansion and therefore means must be provided to effectively block ingress of well fluid which would damage motor parts and ultimately result in premature breakdown.
A problem long associated with the design of submersible motors and seal sections has been that of effectively blocking ingress of ambient well fluid. The difficulty of separation of motor and well fluid was complicated by the miscibility of well fluid with known lubricating and cooling fluids. Also, solutions that effectively blocked ingress of well fluid were poor lubricants or ineffective coolants.
Recent developments have included utilization of an intermediate fluid interposed between the lubricating and cooling fluid and the ambient well fluid in the seal section. The intermediate fluid is insoluble in, and usually heavier than, both the lubricating and cooling fluid and the well fluid. Well fluid drawn into the seal section is separated from the lubricating and cooling fluid by the intermediate fluid. As a result, contamination of the motor is prevented.
Use of an intermediate fluid such as that described necessitates complicated seal section construction, to insure effective blockage of ambient well fluid over prolonged periods. In addition, critical assembly procedures and careful handling of the seal section are required to establish and maintain the proper relationship between the blocking fluid and the lubricating and cooling fluid.
An improved form of submersible motor and seal section uses a single fluid to provide effective lubrication and cooling of the motor, while simultaneously providing an effective barrier to ingress of ambient well fluid.